A known form of pump comprises a housing with an inlet for connection to a source of fluid and an outlet for pumped fluid with the inlet and the outlet being spaced apart around a path of a rotor within the housing. The rotor includes at least one surface forming, with the housing, a closed chamber travelling around the housing to convey fluid around the housing. In this specification, the term “fluid” includes both gases and liquids.
A pump of this kind is disclosed in WO 2006/027548 in which a seal is provided in the housing between the inlet and the outlet to seal against the rotor. A first problem with pumps of this kind is that the housing and the seal are formed separately and then fitted together. As described in WO 2006/027548, the housing may be injection moulded and the seal fixed in the housing using an adhesive. Alternatively, the seal may be moulded with the housing in a 2-shot injection moulding process. This is a problem when there are two or more chambers because, any mismatch at the join between the housing and the seal can cause a leakage between adjacent chambers, particularly at higher pressure differences between the inlet pressure and the outlet pressure and where the apices of the rotor are positioned pressing into the seal. This leakage causes inaccuracy of flow rate of the pump and may allow unwanted backflow through the pump when stopped or at low flow rates.
According to a first aspect of the invention, there is provided a pump comprising a housing, the housing having an interior defining a rotor path, an inlet formed in the housing at a first position on said rotor path, an outlet formed in the housing at a second position on said rotor path spaced from said first position, a rotor rotatable in said housing, at least one first surface formed on the rotor and sealing against said rotor path of the housing, at least one second surface formed on said rotor circumferentially spaced from said first surface and forming a chamber with the rotor path that travels around said rotor path on rotation of the rotor to convey fluid around the housing from the inlet to the outlet, a resilient seal formed in one piece with the housing, located on said rotor path and so extending between the outlet and the inlet in the direction of rotation of said rotor that the first rotor surface seals with, and resiliently deforms, the seal, as the rotor rotates around the rotor path within the housing to prevent fluid flow from said outlet to said inlet past the seal.
A further problem with such a pump arises if there is a mismatch between, first, the force required to form a seal between the rotor and the housing and, secondly, the pressure of the fluid at either the inlet or the outlet. At higher pressures, a greater sealing force is required but, if such a higher force is used at lower pressures, then frictional forces are unnecessarily increased and the torque required to drive the rotor is unnecessarily high. If a lower sealing force is used at higher pressures, then there can be leakage between the seal and the rotor and higher outlet pressures cannot be achieved.
According to a second aspect of the invention, there is provided a pump comprising a housing, the housing having an interior defining a rotor path, an inlet formed in the housing at a first position on said rotor path, an outlet formed in the housing at a second position on said rotor path spaced from said first position, a rotor rotatable in said housing, at least one first surface formed on the rotor and sealing against said rotor path of the housing, at least one second surface formed on said rotor circumferentially spaced from said first surface and forming a chamber with the rotor that travels around said rotor path on rotation of the rotor to convey fluid around the housing from the inlet to the outlet, a resilient seal located on said rotor path and so extending between the outlet and the inlet in the direction of rotation of said rotor that the rotor surface seals with, and resiliently deforms, the seal, as the rotor rotates around the rotor path within the housing to prevent fluid flow from said outlet to said inlet past the seal, the seal having an under surface opposed to a surface of the seal contacted by the rotor, a passage being provided to supply said fluid to said under surface at a pressure that acts to urge the seal against the rotor.
In WO2006/027548, the rotor is provided with one or more chambers with each chamber having a circumferential length that is shorter than the circumferential distance between the inlet port and the outlet port. This limits the volume of fluid that can be pumped.
According to a third aspect of the invention, there is provided a pump comprising a housing, the housing having an interior defining a rotor path, an inlet formed in the housing at a first position on said rotor path, an outlet formed in the housing at a second position on said rotor path spaced from said first position, a rotor rotatable in said housing, one first surface formed on the rotor and sealing against said rotor path of the housing, said first surface having a circumferential length longer than the circumferential length between the inlet and the outlet, a single second surface formed on said rotor circumferentially spaced from said-first surface, having a circumferential length longer than the circumferential length between the inlet and the outlet and forming a chamber with the housing travelling around said rotor path on rotation of the rotor to convey fluid around the housing from the inlet to the outlet, a resilient seal located on said rotor path and so extending between the outlet and the inlet in the direction of rotation of said rotor that the first surface and the single second surface seal with, and resiliently deform, the seal, as the rotor rotates around the rotor path within the housing to prevent fluid flow from said outlet to said inlet past the seal.
In pumps of this kind, the rotor and the chamber of the housing have a generally cylindrical shape with the cylinder of the rotor fitting into and rotating within the cylindrical chamber. The required tightness of fit between the parts is determined during manufacture and is difficult to adjust during assembly or in use.
According to a fourth aspect of the invention, there is provided a pump comprising a housing, a rotor path defined by the housing and within the housing, an inlet formed in the housing at a first position on said rotor path, an outlet formed in the housing at a second position on said rotor path spaced from said first position, a rotor rotatable in said housing, at least one first surface formed on the rotor and sealing against said rotor path of the housing, at least one second surface formed on said rotor circumferentially spaced from said first surface and forming a chamber with the rotor path that travels around said rotor path on rotation of the rotor to convey fluid around the housing from the inlet to the outlet, a resilient seal located on said rotor path and so extending between the outlet and the inlet in the direction of rotation of said rotor that the rotor surface seals with, and resiliently deforms, the seal, as the rotor rotates around the rotor path within the housing to prevent fluid flow from said outlet to said inlet past the seal, the rotor path being frustoconical and the first surface of the rotor being frustoconical and being a mating fit with the rotor path.
In this case, the relative positions of the rotor and the housing may be axially adjustable.